This invention relates to an improvement of a plugging indicator capable of measuring concentration of impurities contained in liquid metal on the principle that impurities contained in liquid metal deposit when the concentration thereof exceeds the saturation solubility.
In a fast breeder reactor or a testing equipment utilizing sodium in which liquid sodium is utilized as a coolant, it is necessary to control or supervise the degree of purity of the sodium by taking into consideration a corrosion check, abrasion check an of a material utilized to construct the equipment, and a leakage detection of water in a steam generator used in the equipment. In order to inspect or monitor the degree of the purity of the liquid sodium, a plugging indicator is generally used.
Generally, the concentration of the impurities contained in the liquid sodium is measured by the plugging indicator wherein the liquid sodium branched from a main conduit of, for example, a testing equipment utilizing sodium into the plugging indicator is cooled to deposit the impurities at a restricted portion so as to increase the pressure drop at the restricted portion, a flow quantity of the liquid sodium is reduced by the pressure drop, and a temperature of the liquid sodium at the restricted portion is measured when the flow quantity thereof is reduced. Thus, the concentration of the impurities contained in the liquid sodium can be determined on the basis of this temperature.
FIG. 1 shows a prior art plugging indicator in which liquid sodium passing through a main conduit 1 of a piece of sodium test equipment is branched by the action of an electromagnetic pump 3 into an inlet or branch pipe 2 and then flows into an economizer or a heat exchanger 5 comprising an inner pipe 9 while the flow quantity of the liquid sodium is measured by a flow meter 4 mounted on the inlet pipe 2. The liquid sodium passing through the economizer 5 is fed through a cooler 6 to a restricted portion called a plugging orifice 7 positioned downstream the cooler 6, where a plugging temperature, i.e. temperature at this restricted portion, is measured by a thermometer 8 disposed thereat.
The liquid sodium then flows into an outlet pipe 10 through the inner pipe 9 of the economizer 5 and returns back into the main conduit 1. The plugging indicator shown in FIG. 1 further includes a by-pass pipe 11 connecting the inlet pipe 2 to the outlet pipe 10. The by-pass pipe 11 is also provided with a restricted portion 12 in connection with the plugging orifice 7.
In the plugging indicator of the type described above, although a suitable A.C. exited electromagnetic pump is used as the pump 3, since it occupies a considerably large space around the inlet pipe 2, the size of the plugging indicator is increased. In addition, in order to deposit a suitable quantity of the impurities contained in the liquid sodium at the plugging orifice 7, a large quantity of liquid sodium has to be branched into the plugging indicator for the reason that a larger quantity of liquid sodium flows into the bypass pipe 11 than that flowing through the plugging orifice 7, so that elements such as the electromagnetic pump and cooler must have a large size. Moreover, the electromagnetic pump 3, flow meter 4, thermometer etc. must be made compact or easily detachable for the purpose of inspecting, maintaining or exchanging the plugging indicator regularly once or twice a year. Particularly, it is difficult to dismount the electromagnetic pump 3 from the inlet pipe 2 without cutting the pipe in the prior art plugging indicator of the type shown in FIG. 1.